Fix -XX:MaxHeapSize setting for Windows

Author: philwebb

build.gradle

@@ -852,7 +852,7 @@ configure(rootProject) {
 
         doLast() {
             def gradleOpts = "-XX:MaxPermSize=1024m -Xmx1024m"
-            def gradleBatOpts = "$gradleOpts -XX:MaxHeapSize=256"
+            def gradleBatOpts = "$gradleOpts -XX:MaxHeapSize=256m"
             File wrapperFile = file('gradlew')
             wrapperFile.text = wrapperFile.text.replace("DEFAULT_JVM_OPTS=",
                 "GRADLE_OPTS=\"$gradleOpts \$GRADLE_OPTS\"\nDEFAULT_JVM_OPTS=")